Pulping process



Patented Mar. 5, 1940 UNITED STATES PULPING PROCESS Floyd 0. Peterson,Midland, Mich., and Louis E. Wise, Winter Park, Fla.

No Drawing. Application October 23, 1936, Serial No. 107,144

14 Claims.

This invention concerns the pulping of lignocellulosic materials, andparticularly relates to a process for the production of alpha-celluloseand other valuable products from ligno-cellulosic materials.

Of the various methods for the digestion of cellulosic materials, thesoda, sulphate, and sulphite processes are the best known and mostwidely used. Of these, the soda and the sulphate processes are alkalinecooks, the soda cook being used primarily in digesting deciduous woodssuch as aspen, birch, white maple, basswood, etc., While the sulphateprocess is well adapted for. digestion of highly resinous coniferouswoods.

In. the soda process the sodium hydroxide is drastic in its action onthe ligno-cellulosic struc-- ture and yields a purified cellulosic fiberwhich is weak and possesses in general inferior chemical properties. Themixture of sodium hydroxide and sodium sulphide in the sulphate processhas a milder action on cellulosic fibers but produces a pulp whichcontains a considerable amount of lignin and other contaminatingproducts. Both of these processes produce a pulp having a comparativelyhigh bleach consumption and not of a sufliciently high grade for use aschemical cellulose in making derivatives thereof.

The sulphite process is an acid cook and pro duces a higher grade pulpthan the above alkaline digestions. The application thereof, however, islimited to the digestion of the less resinous woods, such as spruce,fir, and hemlock, and since it exerts but slight action on the res- 35inous constituents of wood and allows a high percentage of the same topass through into the pulp, thereby creating a problem of resin removalin the, later stages of fabrication.

Each of the above processes yields a waste 40 liquor from which residualpulping agent and valuable by-products such as lignin are difiicult ofrecovery and which are not well adapted to further manufacture. Atpresent such materials are either thrown away or used in the prepara- 5tion of fertilizers, spreading or dispersing agents,

for the preparation of cellulosic derivatives such as ethers and esters.Other objects will be apparent from the following detailed descriptionof certain preferred embodiments of our invention.

We have now-found that ligno-cellulosic material can be pulped bydigesting the same with a pulping fluid comprising a major proportion ofan alkylol-amine. The ligno-cellulosic material, in a suitable state ofdivision, is saturated with, and suspended in, the digesting fluid andthereafter cooked for a period of time, and at temperatures andpressures varying with the type of material being pulped, the amount ofalkylolamine present in proportion to the cellulosic raw material beingtreated, and the degree of digestion desired. When the cellulosicmaterial is sufiiciently cooked, the waste liquor is recovered therefromand the residual pulpy fiber washed, screened, and further purified bybleaching according to any of the known methods. The strength of thispulp, as shown by the beater test (Technical Association Pulp and PaperIndustry ofiicial standard method No. T200M), is as high or higher thanthe strength of pulps otherwise obtained, and other properties such asviscosity are improved, indicating that the mild action of the organicpulping agent causes less degradation and decomposition of thecellulosic portion of the treated raw material than is caused by otherpulping agents ordinarily used. The recovered treating liquor may be (1)reutilized in the pulping of additional ligno-cellulosic materialwithout purification, (2) fractionally distilled to remove therefromunreacted alkylolamines in a substantially pure state and to recovervaluable ligneous residues, or (3) treated with an excess of alcohol,cyclic ether, hydroxyether, or dilute acid, thereby precipitating outthe ligenous bodies, which may be separated, as by filtration. Thelignin bodies obtainable from the above-recovered waste, or black,liquors are valuable raw materials for the preparation of various wellknown lignin type plastics.

While our process is particularly adapted to utilize the alkylol-aminesin substantially pure form, we have found that the crude commercialmixtures of the above, such as are obtained by the reaction of theolefine oxides and ammonia, or by the reaction of the chloroh'ydrins andammonia, may be advantageously employed as pulping agents. The presencein the treating liquor of water or other inert solvent forthe activepulping agent is not prejudicial to the satisfac-' tory performance ofthe pulping action. Other pulping agents such as sodium hydroxide, so-

dium sulphide, etc., may be used in combination with the alkylol-amines,but are not necessary for the carrying out of the reaction. We generallyemploy a treating liquor containing between approximately 70 per cent to100 per cent by weight of alkylol-amine, in most instances analkylol-amine concentration of to per cent of the digesting fluid beingpreferred. The amount of such alkylol-amine composition preferably usedby us in a pulping run is inversely proportional to the concentration ofthe alkylolamine therein. We frequently use 4 to 5 pounds ofalkylol-amine per pound of treated material in order to cover or suspendthe ligno-cellulosic material therein completely. Only a smallproportion of the treating fluid is, however, usedup in such case, andthe recovered liquor may be reutilized a number of times, i. e. until nofree alkylol-amine remains therein, to give a satisfactory pulpingaction. No upper limit on the .amount of alkylol-amine which may bepresent has been determined, since the waste liquors of one run, aspointed out above, may be repeatedly recycled in the process.

In applying our process to the preparation of a high grade cellulosepulp, the wood, preferably in the form of oven-dried chips, isintroduced into a suitable pressure cooking vessel and the treatingliquor added thereto. The cooking vessel is then sealed and-the contentsgradually heated to, and maintained at, the desired digestiontemperature, generally between room temperature and 200 C.,

under the vapor pressure of the reactants at such temperature, until thedesired degree of digestion is obtained. We generally prefer a digestiontemperature of 100 to 180 0., although at temperatures as low as 25 C.appreciable pulping action has been observed. The wood is usuallycompletely pulped in from 4 to 20 hours, although the time of reactionvaries with the amount'and concentration of alkylol-amine present in thetreating liquor, the type of wood being pulped, and the temperature atwhich cooking is carried out. When the wood is properly cooked, thecharge is blown or otherwise removed from the reactor into a suitabledraining or filtering device, 9. 5., a wash pit, wherein the wasteliquor is removed from the solid product. The resulting fibrous pulp iswashed free of digestive liquors, screened, and may thereafter bebleached if desired. Prior to the bleaching step, the crude pulp maybewashed with a dilute aqueous inorganic acid, e. g. 5 per centhydrochloric acid, which step insures amore complete and eificientbleaching action than is obtained if the bleaching step be carried, outwithout such wash. The pulp is then ready for further manufacture intoany desired cellulosic product, such as ethyl-cellulose, celluloseacetate, or regenerated cellulose. If the primary waste liquor is to beused for further digestion it should be diluted as little as possiblewith wash liquors.

The following examples are illustrative of vari- Ous ways in which wehave applied the principle of our'invention, but are not to be construedas limiting the same. 1

Example 1 3 pounds of dried poplar chips and 15 pounds of substantiallypure monoethanol-amine were charged into a pressure cooker equipped withsuitable means for repeatedly circulating the treating liquor throughand over the mass of chips. The temperature of the reaction mixture wasgradually raised to 180 C. and maintained 5 hours.

thereat under a pressure of 30 pounds gauge for 5- hours, after whichthe charge was blown into bodies, and had a beater strength of 114 in'terms of points/100 pounds ream.

The recovered treating liquor, comprising the major portion of the,monoethanol-amine in unreacted form, contained approximately 3.0 percent by weight of the Wood constituents dissolved therein, and wasadapted to be used as a pulping agent in later runs.

Example 2 3 pounds of dried spruce chips were digested, as described inExample 1, with 15 pounds of monoethanol-amine. The duration of the cookwas 5 hours and the maximum temperature 180 C. 1.89 pounds ofdryunbleached pulp was recovered therefrom, having an alpha-cellulosecontent of 84.28 and containing only 0.9 per cent of lignin.

Example 3 3 pounds of dried spruce chips, 12 pounds of monoethanol-amineand 3 pounds of water were charged into a pressure cooking vessel andreacted together at a temperature of 175 C. and under a pressure of 95pounds gauge for approximately The waste treating liquor was separatedfrom the solid products of reaction as described above and the crudepulp washed to remove residual digestive fiuids. The finely dividedproduct was then screened and dried, yielding 2 pounds of unbleachedfibrous material having an alpha-cellulose content of 88.69 per cent.

Example 4 3 pounds of dried poplar chips were digested, as described inExample 1, with a treating solution consisting of 14.4 pounds of1.3-diamino-2-hydroxypropane and 3.6 pounds of water at a temperature of162 C., a pressure of pounds gauge, and for a period of approximately 5hours. 2.28 pounds of dry unbleached pulp was recovered therefrom,having an alpha-cellulose content of 89.53 per cent by weight andcontaining only 0.07

per cent by weight of lignin bodies. Screenings from the above cookamounted to 0.57 per cent based upon the unscreened pulp.

Example 5 2.08 pounds of dried poplar chips, 8.3 pounds ofmonoethanol-amine, 2.08 pounds of water, 0.105 pounds of sodiumhydroxide, and 0.035 pounds of sodium sulphide were charged into apressure cooking vessel and reacted together at a temperature of 180 C.and under a pressure of pounds The resultant crude reaction Example 6 2grams of 60-80 mesh poplar sawdust was refluxed for 5 hours at 180 C.with 200 grams of The suspended solids were then separated from theliquor by filtration, washed successively with hot triethanol-amine, hotwater, alcohol, and ether, and dried,yield ing 1.511 grams of dryunbleached pulp high in alphacellulose and low in lignin.

Example 7 0.939 pounds of dried poplar chips, 6.58 pounds of a highboiling still residue obtained in the fractional distillation of thecrude reaction product of glycerol dichlorohydrin (alpha) and a mmonia,and 1.65 pounds of water were charged into a pressure cooker and reactedtogether at a temperature of C. and under a pressure of 110 poundsgaugefor 5 hours. The resultant crude reaction mixture was worked upsubstantially as described in Example 1, resulting in the isolation of0.43 pounds of dry unbleached pulp high in alpha-cellulose and low inlignin content.

If desired, the digestion process may be interrupted prior to thecomplete delignification of the treated material as described in theforegoing examples. The resulting semi-refined cellulosic bodies havebeen found to be useful in the preparation of manufactured articles suchas ropes, mats, etc., where the presence of a certain amount of ligninin the finished product isnot objectionable.

While the above examples describe only the treatment of poplar andspruce, our process is equally useful in the pulping of other deciduousand coniferous woods such as birch, white maple, basswood, fir, pine,etc. It is also adapted to produce cellulose from suchcellulose-containing raw materials as corn stalks, cotton linters,

wheat straw, and other agricultural waste products.

In a similar manner cellulose may be prepared by the digestion ofligno-cellulosic materials with other alkylol-aminecompounds, solutionsof the same in inert solvents such as water, and mixtures and/orcombinations of the same and I known pulping agents. Among thealkylolamine compounds which may be so employed are diethanol-amine,monopropanol-amine, dipropanol-amine, tripropanol-amine,monobutanolamine, tributanol-amine, ,pentanol-amines, 1.2- diamino 3hydroxy-propane, 1.2-dihydroxy-3- amino-propane, the crude reactionproducts of ethylene chlorohydriin and/or glycerol dichlorohydrin andammonia, mixtures of the above, etc.

The term alkylol-amine as employed herein. and in the appended claims isunderstood to include not only the simple alkylol-amines, such asethanol-amine, etc., but also amino-alkylolamines, such asdiamino-hydroxypropane, etc.

alkylol-amine mixtures without the separation therefrom of theirconstituents, (5) it produces a pulp having a high alpha-cellulosecontent, (6) the pulp so produced has unusually desirablecharacteristics as a starting material'for the preparation of cellulosicderivatives such as ethers, esters, etc., and ('7) the mild action of ithe pulping agent causes less degradation and decomposition of thecellulose in the treated raw material than results in processesordinarily used,

- and thereforeresults in a high yield of desired productrelatively'free from cellulose decomposition products such as sugars,etc., which would tend to reduce its value for chemical use.

Other modes of applying the principle of our invention may be employedinstead of those explained, change being made as regards the methodsherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We therefore particularly point out and distinctly claim as ourinvention:

1. In a process for pulping raw ligno-cellulosic materials, the stepwhich consists in digesting the same with. a treating liquor comprisingat least '70 per cent by weight of an alkylol-amine as an active pulpingagent.

2.In a process for pulping raw ligno-cellulosic materials, the stepswhich consist in digesting the same with a. treating liquor comprisingat least 70 per cent by weight of an alkylol-amine as anactivepulpingagent and thereafter recovering the digestive liquors fromthe solid products of reaction and reutilizing such recovered liquors inthe digestion of additional cellulosic raw material. I

3. In a process for pulping raw ligno-cellullosic materials, the stepswhich consist in digesting the same with a treating liquor comprising atleast 70 per cent by weight of an alkylol-amine as an active pulpingagent, separating the crude pulp therefrom, screening the same, washingthe screened pulp with dilute inorganic acid, and thereafter bleachingthe washed pulp.

.4. In a process for pulping raw ligno-cellulosic materials, the stepwhich consists in digesting the same with a treating liquor comprisingat least '70. per cent by weight of an ethanol-amine as anactive pulpingagent.

'5. In a process for pulping raw ligno-cellulosic materials, the stepswhich consist in digesting the same with a treating liquor comprising atleast 70 per cent by weight of an ethanol-amine as an active pulpingagent at temperatures not in excess of C. under the vapor pressure ofthe reaction at such temperature.

6. In a process for pulping raw ligno-cellulosic materials, the stepwhich consists in digesting the same with a treating liquor comprisingat least 70 per cent by weight of monoethanol-famine as an activepulping agent. if

'7. In a process for pulping raw ligno-cellulosic materials, thestepswhich consist in digesting the same with a treating liquor comprising atleast 70 per cent by weight of monoethanol-amine as an active pulpingagent and thereafter recovering the digestive liquors from the solidproducts of reaction and reutilizing such recovered liq; uors in thedigestion of additional cellulosic raw material.

8. In a process for pulping raw ligno-cellulosic materials, thestepswhich consist in digesting the same with a treating liquorcomprising at least 70 per cent by weight of monoethanol-amine as anactive pulping agent at temperatures not in excess of 180 C. under thevapor pressure of the reaction at such temperature.

9.'In a process for pulping raw ligno-cellulosic materials, the stepswhich consist in digesting the samewith a treating liquor comprising atleast 70 per cent by weight of monoethanol-amine as I an active pulpingagent, separating the crude pulp therefrom, screening the same, washingthe screened pulp with dilute inorganic acid, and thereafter bleachingthe washed pulp.

10. In a process for pulping raw ligno-cellulosic materials, the stepwhich consists in digesting the same with a treating liquor comprisingat least "70 per cent by Weight of the product resulting from thereaction of ammonia with a compound selected from the class consistingof the olefine oxides and the halohydrins as an active pulping agent.

11. In a process for pulping raw ligno-cellulosic materials, the stepswhich consist in digesting the same with a treating liquor comprising atleast 70 per cent by weight of 1.3-diamino-2-hydroxypropane as an activepulping agent at temperatures not in excess of 180 C. under the vaporpressure of the reaction at such temperature.

12. In a process for removing lignin bodies from raw ligno-cellulosicmaterials, the step which consists in digesting the same with a treatingliquor comprising at least 70 per cent by weight of monoethanol-amine asan active pulping agent.

13. In a process for removing lignin bodies from raw ligno-cellulosicmaterials, the step which consists in digesting the same with a treatingliquor comprising at least 70 per cent by weight of triethanol-amine asan active pulping agent.

14. In a process for removing lignin bodies from raw ligno-cellulosicmaterials, the step which consists in digesting the same with a treatingliquor comprising at least 70 per cent by weight of1.3-diamino-Z-hydroxy-propane as an active pulping agent. FLOYD C.PETERSON.

LOUIS E. WISE.

